Steady Under Pressure: Distillation Pressure Control - Method 22

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Method 22: 3E :  Control condenser inlet coolant temperature and composition. Evaporative cooler.

Method: Vary heat flux. Vary temperature and relative humidity of air.
Process: Net vapor rate zero. Evaporative cooler.
Advantages: Exchanger film temperatures at maximum.
Disadvantages: Local pump required. Response may be slow due to system liquid inventory.
Application: Condenser always runs at maximum temperature consistent with duty removal. This can be useful to prevent localized solidification in some processes. Often used in climates that may have very cold operating days to prevent plugging from solids.
Configuration notes: The evaporative condenser essentially includes the cooling tower in the condenser. It may include a dedicated bypass fan to improve control. Process industries have been moving away from the evaporative condenser towards cooling tower provided water over the last 20 to 30 years.
Operation: Water humidification into the air controls the duty removal. Controlling the net air rate to the system varies the amount of water that can vaporize to remove heat (exit air at 100 percent relative humidity). Unit LMTD decreases with lower air rates.

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This page updated 03 April 2000.
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